The smallest stag beetles (Coleoptera, Lucanidae): hidden paleodiversity in mid-Cretaceous Kachin amber from northern Myanmar

Abstract

The fossil record of stag beetles (Lucanidae), especially in Mesozoic amber, is sparse. Four additional fossil lucanids preserved in mid-Cretaceous Kachin amber from northern Myanmar are here reported. All of these species are included in the primitive subfamily Aesalinae, and have been identified as: Protonicagus mandibularissp. nov. (tribe Nicagini); Cretognathus minutissimusgen. et sp. nov. (tribe Ceratognathini); Ceratognathini gen. et sp. indet. 1 (provisional assignment); and Ceratognathini gen. et sp. indet. 2 (provisional assignment). Except for Protonicagus mandibularissp. nov., the stag beetles appear to be connected to the continent of Gondwana, as with the Kachin amber paleofauna. More interestingly, these species have significantly smaller bodies than the extant species, with three of them measuring less than 3 mm, which makes them the smallest known species of Lucanidae. This finding is congruent with a trend toward miniaturization in several unrelated lineages of Kachin amber beetles, and it shows hidden paleodiversity of stag beetles during the Cretaceous.